High Lockout
F.00 on Vaillant ecoTEC sustain

Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water leaving the unit.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flow temperature sensor interruption

What causes this fault?

This fault occurs when the boiler's main control board loses the electrical signal from the sensor that monitors the heat of the water leaving the unit. It is usually caused by the sensor itself failing due to age, or damage to the internal wiring that prevents information from reaching the central computer.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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